The Orbital Transfer Vehicle is a reusable space tug, powered by LOX/LH2 engines and equipped with an aerobrake allowing it to be returned for refueling and reuse at an orbiting space station. It is an integral part NASA's Destiny second generation space station, lunar and Mars exploration plans in the 1990's and beyond.
Destiny is Liberty twin backup module. It was build as an insurance in the case Liberty Saturn V blew up. With Liberty safely in orbit, Destiny become his successor to be launched circa 1995. NASA growing frustration with Liberty mean very ambitious plans were drawn around Destiny. It might be a space dock for advanced space tugs.
NASA conducted advanced studies of what was then called the Space Tug in the early 1970's. However all elements of NASA's future vision of space exploration were cancelled to allow funds for development of the Space Shuttle. When the Shuttle was canned in 1971, the tug returned but only as a low-cost, low-performance Agena for space station Liberty assembly. It was subcontracted to the European Space Agency.
After Liberty assembly was complete NASA began studying the tug again, now dubbed the Orbital Transfer Vehicle (OTV). The OTV evidently benefited from all the experience massed with Agena operations. The Agena was extremely versatile and successful as a space tug, but its storable propulsion system lacked performance to GEO and beyond.
Studies in the 1970's had already considered use of an aerobrake heat shield. This would allow the Tug, on its return from geosynchronous orbit, lunar orbit, or interplanetary trajectories, to use the earth's atmosphere to brake to orbital velocity, after which it would maneuver, then rendezvous and dock with a Space Station for refurbishing, refueling, and reuse. Use of aerobraking offered significant weight savings in comparison to pure rocket braking to return to the station. An Agena could test aerobraking and aerocapture.
One of Destiny most important missions will be to serve as a space harbor for missions to geostationary orbit, where most communications satellites are located. Large satellites would be delivered to Destiny from Earth by the Shuttle II for final assembly and checkout. An Orbital Transfer Vehicle would then transport the satellite to geostationary orbit. The OTV would be permanently based at the space station in low Earth orbit.
The $1-billion OTV is planned to form part of the Destiny second generation Space Station infrastructure in the mid-1990s. Important missions include delivery of large satellites (initially weighing 8 tons) to geostationary orbit, retrieval of satellites for servicing at the Space Station and eventually manned sortie missions to GEO. In turn GEO is seen as a backdoor to lunar orbit. NASA intend to use the lucrative GEO satellite market to bootstrap lunar exploration through the OTV, since delta-v were roughly the same, 4.1 km/s.
There will be both Space Station-based OTVs as well as vehicles that would be returned to Earth by the Shuttle II for servicing. A ground-based OTV could be operational by 1992 and a Space Station-based version by 1994-95.
NASA/JSC recently awarded studies contracts to examine the effects of advanced manned lunar and unmanned planetary missions on the Destiny Space Station. The basic idea is to use the Station with a fleet of reusable OTV's for ambitious missions such as the unmanned biconic 8,890kg Mars sample return vehicle.
The space tug would require a propellant load of 27,760 kg for this mission, which is scheduled for a November 1996 launch. Mission requirements for other envisioned OTV planetary missions are summarized below. Both reusable OTV's (which would return to the Station for reuse) and Expendable OTVs, which do not carry a 3,731 kg aerobrake, were planned (coded E or R in the list). All missions except Mars Sample Return would used the Voyager Mk.II robotic spacecraft as payload carrier.
- Titan Probes/Saturn Orbiter. Launch: 4/1993. C3 velocity requirement: 50.5 km2/sec2. Requirement: 1 Expendable OTV with 6.34t payload, 53.54t total mass, 41.81t OTV propellant, 48.15t net new payload elements required to be launched for the mission. 109 astronaut man-hours would be required for payload fueling and integration.
- Mercury Orbiter. Launch: 6/1994. C3 velocity requirement: 18.7 km2/sec2. Requirement: 1 Reusable OTV with 5.63t payload, 41.62t total mass, 28.90t OTV propellant, 34.53t net new payload elements required to be launched for the mission. 106 astronaut man-hours would be required for OTV refurbishment, aerobrake removal, payload refueling and integration.
- Ceres Sample Return. Launch: 10/1994. C3 velocity requirement: 9.9 km2/sec2. Requirement: 1 Reusable OTV+1 Expendable OTV with 43.57t payload, 131.59t total mass, 75.47t OTV propellant, 119.04t net new payload elements required to be launched for the mission. 247 astronaut man-hours would be required for OTV refurbishment, aerobrake removal, payload refueling and integration, and sample retrieval.
- Mars Sample Return. Launch: 11/1996. C3 velocity requirement: 9.0 km2/sec2. Requirement: 1 Reusable OTV with 8.89t payload, 44.03t total mass, 27.76t OTV propellant, 36.65t net new payload elements required to be launched for the mission. 138 astronaut man-hours would be required for OTV refurbishment, aerobrake removal, payload refueling and integration, and sample retrieval.
- Kopff Sample Return. Launch: 7/2003. C3 velocity requirement: 80.7 km2/sec2. Requirement: 1 Reusable OTV+1 Expendable OTV with 8.38t payload, 92.49t total mass, 71.51t OTV propellant, 79.89t net new payload elements required to be launched for the mission. 236 astronaut man-hours would be required for OTV refurbishment, aerobrake removal, payload refueling and integration, and sample retrieval.
The OTV primary mission would deliver 9t to geostationary orbit using a single stage and 18t payloads to lunar orbit using two OTV space tugs in tandem. Each OTV has a mass of 7t empty and carry up to 42t of oxygen & hydrogen propellant (engine Isp=455.4s). The primary lunar mission payload would be modules for a permanent 18-crew Moonbase in 2005-2015; as required by the plan developed by a Johnson Space Center team lead by Barney Roberts in 1984. A 3.5t expendable landing vehicle with 13.5t of propellant would land 17.5t Space Station-derived modules on the lunar surface. 100t of propellant would have to be launched per lunar mission; NASA proposed to develop a 2nd generation Saturn V heavy-lift launch vehicle for this purpose. The Shuttle II would transport the empty 21,000-kilogram lunar lander+payload to the Space Station, where they would rendezvous with the 100t propellant module. OTV's and other hardware would be integrated at a Space Station-based spacedock.
For manned lunar crew exchange missions, the OTV would carry 5,500kg or 8,000kg cylindrical passenger modules for 4 or 6 astronauts, respectively. The passenger OTV would rendezvous in lunar orbit with a 10,000kg 6-crew lunar lander which would be fueled by 4t of hydrogen brought from Earth and oxygen produced from lunar soil. This would reduce the launch requirement from Earth. The manned missions would also carry an expendable 7,600kg lander plus 3,250kg logistics module for life support of four crew members during lunar launching and landing.
The 1984 NASA/JSC plan calls for the development of OTVs and lunar landers in 1995-2003 to permit the creation of small semi-permanent manned camp on the lunar surface in 2005-2006. The ultimate goal would be a self-sustaining moonbase by 2017-18. NASA/Johnson also regards the space tug as an integral component of its Destiny Space Operations Center plan.
A modular OTV design was proposed by General Dynamics in 1984. Spherical tanks contained liquid hydrogen and oxygen propellant for the engines; three sets would be carried for manned or heavy-lift missions while one set would suffice for delivering smaller unmanned payloads.
A concept is equipped with a huge disc-shaped aeroshell which slows the vehicle down as it pass through the Earth's upper atmosphere. The space tug could then return heavy payloads from geostationary or lunar orbit without using any fuel to rendezvous with the low Earth orbit space station. Another space tug concept would have had better maneuverability thanks to its aerodynamic shape, but it would also weigh more.
A variant of the Orbital Transfer Vehicle concept is named the Lunar Transfer Vehicle to stress its importance for manned lunar base missions. The LTV would provide transportation between Space Station Destiny and lunar orbit. The LTV would transport a crew of four astronauts in an 8.4-metric ton passenger module as well as up to 22.4t of cargo in two external containers. Propulsion in this version was provided by four 89 kiloNewton-thrust AES engines (481s Isp). The oxygen and hydrogen propellant (129.8t in all) would be stored in four 1.45-metric ton expendable fuel tanks. The empty tanks would be discarded in Earth and lunar orbit to reduce the mass of the vehicle; 10% more fuel would have to be carried if the tanks were returned to Earth orbit for reuse. The basic, reusable LTV weights 8.1t empty and consists of a propulsion / propellant / avionics module that hold 7t of propellant for returning to Space Station Destiny from lunar orbit. A large aerobrake protects the vehicle as it performs an aerocapture maneuver to kill off excess speed by passing through the Earth's upper atmosphere. This would save rocket propellant but the aerobrake would be heated to more than 1000K so it is to be made of advanced thermal protection materials. Aerobrake reuse for five missions is assumed, with refurbishment and verification at Space Station Destiny.
Beginning in late 1983, a team of engineers and scientists from NASA’s Johnson Space Center (JSC) and the Jet Propulsion Laboratory jointly defined a Mars Sample Return spacecraft and mission plan. Among their proposed follow-on study objectives for Fiscal Year 1985 was to define Mars sample quarantine methods and any associated risks. In addition, the team recognized the need to rapidly recover the Mars sample after its arrival at Earth.
JSC’s Solar System Exploration Division explored varied options for retrieving a Mars sample following its return to Earth’s vicinity. Capture by an Agena and sample repackaging into a heavily modified Big Gemini crew module were considered, but JSC first and foremost wanted to place its space station as a quarantine facility were Mars samples could be studied before return to Earth. JSC engineers asked, what could a space station do a ground-based laboratory couldn't ? The most salient argument (reminiscent of the Andromeda Strain) was that a space station would be out of Earth biosphere.
Option 1 was Minimal Sample Analysis. A a small sub-sample would removed from the sample canister for “minimal” biological analysis. There was some question as to how much use a minimal analysis would be.” Alternatively, astronauts would remove a sub-sample and heat it enough to kill martian microbes while preserving evidence of their existence before the sample canister was send back to Earth for analysis. The remainder of the sample - and, possibly, the Station crew - would remain in quarantine until scientists in the PSRL had checked out the sub-sample.
Option 2 consisted of a purpose-built Orbital Quarantine Facility (OQF) module that would be capable of supporting long-term detailed sample analysis on much the same scale as the Earth-based laboratory. If researchers working in the Antaeus module found that the Mars sample was safe, then it would be transported to Earth. If, on the other hand, the sample were found to contain harmful martian microbes, then the Antaeus module would be detached and boosted into a 1270-kilometer-high long-term orbit using an Agena In the event that harmful microbes escaped from the Antaeus module and contaminated the Space Station, then multiple Agena space tugs could boost the entire Station into a 650-kilometer-high orbit. JSC estimated that orbit-raising maneuvers could extend the orbital lifetime of the Antaeus module or Station for long enough to permit NASA to develop a large rocket stage that could boost the contaminated Antaeus module or Station into interplanetary space. They mentionned that Agena space tug technology could easily be adapted to a high energy Centaur.
Option 3 1/2 Quarantined Space Station would be nearly identical to option 2 except that the Station modules that would support the scientists analyzing the sample in the Antaeus module would be isolated from the rest of the Station. This would be achieved by closing pressure hatches between the two halves of the Station and slightly reducing air pressure in the quarantined modules.
Option 4 would be a dedicated, independent space station in Earth orbit This option would make unnecessary the laboratory on Earth since all quarantine and analysis would take place in Earth orbit. It was without a doubt the safest, biologically, of all the options but added that the price paid for this additional safety seems unreasonably high. JSC however mentionned that Liberty backup core module, Destiny, was already build and in storage. Further studies would explore how it could be turned into a full-blown Mars sampling laboratory.
JSC desperate efforts to link their space station to Mars Sample Return were born out of despair. With Liberty already in orbit Congress was very reluctant allowing funding of Destiny. Yet Liberty, as build, was hated by JSC – it was not the ambitious space shipyard they dreamed about. The orbital quarantine study had been a joint JSC – JPL work, together with a private companie with the name of Science Applications Incorporated (SAIC). It was from SAIC that the next major breakthrough was to come.
John Niehoff was manager of the Space Sciences Department at Science Applications International Corporation (SAIC) in Schaumburg, Illinois, when he presented his Integrated Mars Unmanned Surface Exploration (IMUSE) strategy to the National Academy of Science Space Science Board Major Directions Summer Study on 30 July 1985. He proposed employing reusable automated spacecraft with designs “deeply rooted” in planned U.S. space station technology to carry out a complex, evolving series of automated Mars Sample Return (MSR) missions between 1996 and 2016.
His work had its origins in the 1984 joint Jet Propulsion Laboratory/NASA Johnson Space Center MSR study. Niehoff and SAIC provided both the JPL/JSC MSR study with planning and engineering support.
Just like JSC, Niehoff intended to link MSR with the Space Station, albeit in a different maner. The Agena space tug was extending the space station range higher and higher, to GEO and even beyond. Niehoff calculations showed that a Liberty-based Agena could retrieve a Mars sample canister in high Earth orbit and bring it back to the space station. As a proof-of-concept Niehoff proposed to retrieve on the three Pioneer solar probes in heliocentric orbit for three decades. He might have been influenced by ISEE-3 new mission to a comet, the brainchild of Robert Farquhar.
Niehoff noted that pioneering hyperbolic rendezvous was extremely important. He cited the FLEM study of the 60's – Flyby Landing Excursion Mode.
FLEM stated that, in the “standard stopover mode,” all major maneuvers would involve the entire Mars spacecraft. Since the main spacecraft would not have to brake into and out of Mars orbit, huge propellant savings were possible, drastically reducing the number of heavy rocket expensive launches.
One part of the FLEM spacecraft, the parent spacecraft, would not capture into Mars orbit. The other part, the excursion module, would capture into Mars orbit using chemical rockets or, perhaps, by skimming through Mars’s atmosphere behind an aerocapture heat shield. Assuming that the mission took place as planned, the excursion module would ignite its rocket motors as the parent spacecraft passed Mars to depart Mars orbit and catch up with it. Following hyperbolic rendezvous, docking, and crew transfer, the excursion module would be cast off.
Niehoff’s IMUSE spacecraft – which he dubbed an Interplanetary Platform (IP) – would transport smaller vehicles between Earth and Mars. At Mars, it would drop probes; while at Earth, it would handle Mars samples to an Agena tug.
The Interplanetary Platform would provide planetary payloads with “keep-alive” solar cell-generated electrical power, thermal control, course-correction propulsion, and other requirements typically provided by a throwaway spacecraft bus. The IP would cut costs over the course of the IMUSE program because it would need to be launched onto its interplanetary path only once. As the IP flew without stopping past Mars or Earth, the smaller vehicles would separate to land on or go into orbit around the planet or would leave the planet to rendezvous and dock with the IP.
He described a pair of IMUSE scenarios. In both, the IP would follow Versatile International Station for Interplanetary Transport (VISIT) cycler orbits, which would, Niehoff explained, be “simultaneously resonant with both Earth and Mars.” A spacecraft in a VISIT-1-type orbit would circle the Sun in 1.25 Earth years, which meant that it would encounter Earth four times in five Earth years and Mars three times in two Mars years. A VISIT-2-type orbit, on the other hand, would need 1.5 Earth years to complete. A spacecraft on a VISIT-2 path would encounter Earth twice in three Earth years and Mars five times in four Mars years.
Niehoff concluded saying that the diminutive Agena could be replaced by a high-energy Centaur or a dedicated Orbital Transfer Vehicle. Space station Liberty currently acted as a fuel depot transfering storable propellants to Agenas. In the future Destiny would do the same, albeit with high-energy liquid hydrogen and oxygen.
The recovery of Pioneer 7 (1992)
The mission was the brainchild of two Goddard engineers. Robert Farquhar was an expert of libration points and low-energy trajectories. Frank Cepollina expertise was in-space servicing. Pioneer 7 had been launched in August 1966. It was a joint JSC – Goddard project inspired by Robert Farquhar ISEE-3 “ICE” cometary mission of 1982-1986.
On March 20, 1986 Pioneer 7 flew within 12.3 million kilometers of Halley's Comet and monitored the interaction between the cometary hydrogen tail and the solar wind. The Deep Space Network atempted to contact all three Pioneer probes, and all three were found to be still functionning.
Frank Cepollina arranged with JSC for the Agena. JSC goal was to prove lunar swingby hyperbolic rendezvous, space tug, satellite retrieval from heliocentric orbit.Long term objectives were to proof of concept for Destiny as a link for planetary exploration through space tugs and semi- cyclers – an orbital quarantine facility. Further missions included flights to an asteroid (pushed by Jim Benson) and to the Moon (SDIO).
Mission profile
A modified Agena space tug is launched by a Thorad to space station Liberty
On orbit refueling of storable propellants
Fire the rocket engine, climb to Earth escape and cislunar space
Perform a lunar swingby to get into an heliocentric orbit
Hyperbolic rendezvous with Pioneer 7 (6 and 8 are backup options)
Catch Pioneer 7 with a robotic arm
Restart the engine a first time to get back in the direction of Earth neighborough
Propulsive bracking back into space station Liberty orbit
Thorough examination of the old solar probe by EVA astronauts
Eventually, packaging of the small probe into a modified Big Gemini crew module (through a wider hatch in the heatshield)
Return to Earth for further examination
Final resting place: the Smithonian
The mission has a lot of firsts
- propellant refueling at Liberty
- first lunar swingby by a space tug
- hyperbolic rendezvous, docking and retrieval
- propulsive braking from interplanetary space to low Earth orbit
- first interplanetary probe brought back to Earth surface after decades in deep space
